What question did this study set out to answer?

The study examines IL4I1+ macrophages' role in driving intestinal fibrosis in Crohn's disease and the underlying molecular mechanisms.

January 23, 2026

P0002IL4I1+ Macrophages Drive Intestinal Fibrosis in Crohn’s Disease through the KynA-AhR Pathway

Key Points

The study examines IL4I1+ macrophages' role in driving intestinal fibrosis in Crohn's disease and the underlying molecular mechanisms.
Collected fibrotic and non-fibrotic intestinal tissues from Crohn’s disease patients.
Characterized myeloid cell subpopulations using single-cell RNA sequencing and spatial transcriptomics.
Validated macrophage distribution with immunohistochemistry and flow cytometry, and assessed the effects on fibroblasts in co-culture systems.
Utilized liquid chromatography-mass spectrometry and AhR nuclear translocation assays to analyze signaling pathways.
IL4I1+ macrophages significantly increased in fibrotic tissues, co-localizing with ECM-high fibroblasts.
Expressions of IL4I1, COL1A1, and α-SMA were upregulated in fibrotic tissues confirmed by clinical samples.
Functional assays demonstrated IL4I1+ macrophages promoted fibroblast activities including proliferation and ECM synthesis through KynA and AhR activation.

Abstract

Abstract Background Intestinal fibrosis in Crohn’s disease (CD) is a primary cause of intestinal obstruction and surgical intervention, with a lack of effective anti-fibrotic drugs. This study aims to investigate the role and molecular mechanism of IL4I1+ macrophages in CD intestinal fibrosis, providing new strategies for targeted therapy. Methods Fibrotic and non-fibrotic intestinal tissues from CD patients were collected. Myeloid cell subpopulations were characterized by integrated single-cell RNA sequencing (scRNA-seq) and spatial transcriptomics (ST). Immunohistochemistry (IHC), multiplex immunofluorescence (mIF), and flow cytometry (FACS) were used to validate the spatial distribution of IL4I1+ macrophages and their interaction with fibroblasts. A co-culture system of patient-derived intestinal IL4I1+ macrophages and fibroblasts was established to assess their effects on cell proliferation, migration, invasion, and extracellular matrix (ECM) deposition. Liquid chromatography-mass spectrometry (LC-MS) and AhR nuclear translocation assays were employed to investigate the downstream KynA-AhR signaling axis. Results Integrated scRNA-seq and ST analysis revealed a significant increase in IL4I1+ macrophages in CD fibrotic tissues, showing spatial co-localization with ECM-high fibroblasts expressing high levels of COL1A1 and FN. Clinical sample validation confirmed upregulated expression of IL4I1, COL1A1, and α-SMA in fibrotic tissues. FACS detected an increased proportion of IL4I1+ macrophages, and mIF further revealed the co-localization of CD68+IL4I1+ macrophages with COL1A1+α-SMA+ fibroblasts in fibrotic areas. Functional experiments demonstrated that IL4I1+ macrophages promoted fibroblast proliferation, migration, invasion, and ECM synthesis. Further studies found that IL4I1+ macrophages secrete kynurenic acid (KynA) via the non-classical kynurenine pathway, activating aryl hydrocarbon receptor (AhR) nuclear translocation in fibroblasts. Exogenous KynA mimicked the pro-fibrotic effects, whereas AhR knockout in fibroblasts reversed the IL4I1+ macrophage-mediated promotion of ECM synthesis. Conclusion IL4I1+ macrophages are specifically enriched in CD intestinal fibrotic areas and drive ECM deposition and fibrosis progression by secreting KynA to activate the AhR signaling pathway in fibroblasts. Targeting the IL4I1-KynA-AhR axis may provide a novel direction for anti-fibrotic therapy in CD. Conflict of interest: Ms. Wang, Haiyang: Grants Zhang, Hongjie: Provision of writing assistance, medicines, equipment, or administrative support Fan, Zhining: Provision of writing assistance, medicines, equipment, or administrative support Liu, Li: Grants

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